Various types of clutches are used to transmit torque in vehicles. In a vehicle having an automatic transmission, for example, multiple clutches are used to engage or disengage selected gearsets in real time to obtain desired gear ratios. The primary clutches provided for this purpose are generally formed of friction plate clutches that include a plurality of inner or drive plates splined to a rotatable hub. A housing or case is coaxially aligned with the hub and supported for rotation independently of the hub. A plurality of outer or driven plates are splined to the housing or case and are interposed between the drive plates, such that the drive and driven plates are alternately arranged on a common axis. The drive plates generally include a friction material on one or both sides of the plates. An actuator may include a hydraulic piston adapted to apply a force that presses the drive and driven plates into engagement, thereby permitting torque to be transferred from the hub to the housing.
It is also known to utilize a mechanical locking clutch, such as a dog clutch, in combination with the described friction plate clutch. The dog clutch offers a positive lock of drive and driven members, without risk of slippage while under full torque loads upon full clutch engagement. Such dog clutches provide opportunities for reducing the numbers of plates used in the friction plate clutch to achieve a maximum desired torque. Such plate reduction is particularly pertinent to times when the clutch is unengaged and idling, as then the plates tend to generate a parasitic drag torque with resultant undesirable heat and wear. The latter occurs due to viscous shearing action between drive and driven plates that are often rotating at different speeds relative to one another. Such drag torque adversely affects vehicle fuel economy, and the use of excessive numbers of plates can exacerbate this problem.
Synchronizing clutches that employ both friction plates and dog or mechanical connection are well known. U.S. Publication 2011/0155530 A1, for example, discloses a composite clutch utilizing both friction and dog clutch elements. The improvements noted and disclosed herein may, however, improve operational characteristics associated with transitioning between friction and dog clutch operating modes with respect to such composite clutches.